1. Field of the Invention
The present invention relates to a display apparatus. In particularly, the present invention relates to an optical projection display apparatus.
2. Description of Related Art
FIG. 1 shows an optical projection apparatus 100 disclosed by U.S. Pat. No. 6,784,946. The optical projection apparatus 100 comprises an illuminating system 110, a reflective light valve 120, a prism 130, a lens set 140 and a projection lens set 150. The illuminating system 110 is used for providing a light beam that sequentially passes through the prism 130, the lens set 140, and then is incident to the reflective light valve 120. The reflective light valve 120 is a digital micro-mirror device (DMD). The reflective light valve 120 is used for converting the light beam 112 into a plurality of sub-image beams 112a, and then reflecting the sub-image beams 112a to the lens set 140. Then, the sub-image beams 112a are incident to the projection lens set 150 for imaging.
One key point for determining whether the imaging of the optical projection apparatus is clear is that whether or not the sub-image beams 112a is precisely projected to the projection lens set 150. This factor is determined by an arrangement of a relative position between the prism 130 and the lens set 140. If the relative position between the prism 130 and the lens set 140 has an error, the incident angle of the light beam 112 is changed. Thereby, the sub-image beams 112a deviates and is not correctly projected into the projection lens set 150. Although the elements of the optical projection apparatus 100 become miniaturized, the accuracy for assembling the optical projection apparatus 100 is not as good as expected. Therefore, the image quality is degraded.
FIG. 2 shows an optical projection apparatus 200 disclosed by U.S. Pat. No. 6,471,356. The optical projection apparatus 200 comprises an illuminating system 210, a reflective light valve 220, a total internal reflection (TIR) prism 230, a lens 240 and a projection lens set 250. The illuminating system 210 is used for providing a light beam 212, sequentially passing through the TIR prism 230, the lens 240 and the reflective light valve 220. The reflective light valve 220 is a DMD. The reflective light valve is used for converting the light beam 212 into a plurality of sub-image beams 212a, and then reflecting the sub-image beams 212a back to the lens 240. The projection lens 250 has a pupil 252 located within or at a side surface of the projection lens set 250. The sub-image beams 212a are converged at the pupil 252 and incident to the projection lens set 250 for imaging.
FIG. 3 is a schematically enlarged diagram of the reflective light valve, the total internal reflection prism and the lens shown in FIG. 2. Referring to FIGS. 2 and 3, when the light beam 212 is incident to the reflective light valve 220, such as a DMD (not shown), the reflective light valve 220 has a plurality of micro-mirrors (not shown) to convert the light beam 212 into a plurality of sub-image beams 212a. The ON-state micro-mirrors reflect the light beam 212 back to the lens 240, and the OFF-state micro-mirrors deviate the light beam 212 away from the lens 240. The lens 240 converges the sub-image beams 212 on the pupil 252, and then the sub-image beams 212a are incident to the projection lens set 250 for imaging. In addition, the optical projection apparatus 200 further comprises an aperture stop 260, which corresponds to the pupil 252 and is located within or at the side surface of the projection lens set 250. The function of the aperture stop 260 is used for determining a diameter of a light cone that light emitted from the optical projection apparatus 400 passes through, and an illuminance of the passed light. Further, the aperture stop 260 is further used for blocking environmental stray light from entering the projection lens set 250 to form images, so as to prevent blurred images. Since the TIR prism 230 is set within the optical projection apparatus 200, the design of an optical path is simplified and error in angle deviation for the optical path becomes smaller.
However, it is unavoidable that stray light is likely to occur in the optical projection apparatus 200. In the aforementioned apparatus, the pupil 252 and the aperture stop 260 are set at the rear end of the entire optical path to block and filter the stray light. However, such arrangement decreases the function of the aperture stop 260, and consequently, a large portion of the stray light is not efficiently blocked and the image quality is degraded.